Synthesis and characterization of a [Mn12O12(O2CR)16(H2O)4] complex bearing paramagnetic carboxylate ligands.: Use of a modified acid replacement synthetic approach

A new modified approach for the synthesis of Mn-12 clusters, based on the use of complex [Mn12O12(O2C'BU)(16)(H2O)(4)] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us to obtain complex [Mn12O12(O2CC6H4N(O-.) 'BU)(16)(H2O)(4)] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn12Ac (1). Complex 3 bearing open-shell radical units, was prepared to increase the total spin number of its ground state, and consequently, to increase T-B, with the expectation that the radical ligands may couple ferromagnetically with the Mn-12 core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn-12 core to yield a S = 2 magnetic ground state.